The present invention relates to an extrudable composition for forming a nonwoven web (e.g., a film, sheet, etc.) of a pressure sensitive elastomer adhesive, methods of utilizing such composition, and products formed utilizing such composition. More particularly, the present invention relates to fibrous nonwoven webs, especially meltblown webs, of such composition, and stretch bonded laminates using a web of such composition. Moreover, the present invention relates to methods of forming nonwoven webs, particularly fibrous nonwoven webs, utilizing such composition and use of such webs for forming stretch bonded laminates, wherein such elastomeric web is stretched and, while stretched, bonded to at least one layer of gatherable material.
For some time those in the art have been attempting to form elastomeric resins into fibrous nonwoven elastomeric webs. For example, attempts have been made to form fibrous nonwoven elastomeric webs utilizing KRATON.RTM.G elastomeric resins. KRATON.RTM. is a trademark of Shell Chemical Company of Houston, Tex., for various polystyrene/poly(ethylene-butylene)/polystyrene elastomeric block copolymers. In U.S. Pat. No. 4,323,534, it is disclosed that the KRATON.RTM.G rubber resins are too viscous to be extruded alone without substantial melt fracture of the product; and that various of the KRATON.RTM.G resins should be blended with a fatty chemical such as stearic acid prior to extrusion and, e.g., meltblown, so as to overcome the viscosity problem. However, physical properties of the product obtained by this process, for example, a nonwoven mat of meltblown fibers, were apparently unsatisfactory because, after formation of the nonwoven web, substantially all the fatty chemical is leached out of the nonwoven web of extruded microfibers by soaking the web in alcohols having a good ability to solubilize the fatty chemical utilized.
In order to overcome, e.g., the above-stated viscosity problems, it has been proposed to form elastomeric block copolymer materials into nonwoven elastomeric products by providing extrudable elastomeric compositions which are blends of (1) an A-B-A' block copolymer, where "A" and "A'" are the same or different and are each a thermoplastic polymer endblock which includes a styrenic moiety such as a poly(vinyl arene) and where "B" is an elastomeric poly(ethylene-butylene) midblock, with (2) a polyolefin which, when blended with the A-B-A' block copolymer and subjected to appropriate elevated pressure and elevated temperature conditions, is extrudable in blended form, with the A-B-A' block copolymer. The presence of the polyolefin in the blend serves to reduce the viscosity of the composition as compared to the viscosity of the pure A-B-A' block copolymer and thus enhances the extrudability of the composition. Such blend must be a composition which, after extrusion, solidifies to form elastomeric products.
Thus, utilizing a blend of the block copolymer and the polyolefin, the composition can be extruded at conventional temperatures and pressures, and, in particular, can be extruded at temperatures lower than temperatures at which the block copolymers degrade or burn. The extrudable composition may be formed into a variety of products such as, for example, fibrous nonwoven elastomeric webs preferably having microfibers with an average diameter not greater than about 100 microns, and preferably having an average basis weight of not more than about 300 grams per square meter, for example, an average basis weight of from about 5 grams per square meter to about 100 grams or more per square meter. In connection with this extrudable composition, note U.S. Pat. No. 4,663,220 which issued on May 5, 1987 of Tony J. Wisneski and Michael T. Morman, for "Polyolefin-Containing Extrudable Compositions and Methods for Their Formation Into Elastomeric Products", the contents of which are incorporated herein by reference.
Moreover, uses for nonwoven elastomeric webs, either by themselves or as part of a composite laminate, are being investigated. Thus, composite fabrics comprising at least one layer of nonwoven textile fabric mechanically secured to an elastomeric layer are known. For example, U.S. Pat. No. 4,446,189 discloses textile laminate materials comprising an inner layer of elastic material, such as a polyurethane foam of a thickness of about 0.025 inches, needle punched at a plurality of locations to a nonwoven textile fabric layer. The needle punched superposed layers are then stretched within the elastic limits of the elastic layer to permanently stretch the nonwoven fabric layer material needle punched thereto. When the elastic layer is allowed to relax and return to substantially its condition prior to being stretched, the nonwoven fabric layer is stated to exhibit increased bulk by virtue of the relaxation of its permanently stretched fibers.
Moreover, U.S. Pat. No. 4,209,563 discloses a method of making an elastic material which includes continuously forwarding relatively elastomeric fibers and elongatable but relatively non-elastic fibers onto a forming surface and bonding at least some of the fiber crossings to form a coherent cloth which is subsequently mechanically worked, as by stretching, following which is it allowed to relax. As described by the patentee at column 8, line 19 et seq, the elastic modulus of the cloth is substantially reduced after the stretching, resulting in the permanently stretched non-elastic filaments relaxing and looping to increase the bulk and improve the feel of the fabric. This patent discloses that the bonding of the filaments to form the coherent cloth may utilize embossing patterns or smooth, heated roll nips.
U.S. Pat. No. 2,957,512 concerns a method of producing elastic composite sheet materials and discloses that a reticulated, fibrous web formed of an elastomeric material such as rubber, including butadiene-styrene copolymers, may be utilized as the elastic ply of a composite material. The patent discloses that a relaxed sheet material ply may have a fibrous web of elastomeric material of smaller area than the sheet material stretched so as to conform it in area to the area of the sheet material and the plies are bonded together at spaced points or areas. Upon allowing the fibrous elastomeric ply to relax, the composite body is stated to assume a structure of a fibrous web of elastomeric material bonded at spaced areas or lines to a ply of a creped or corrugated flexible sheet material.
Furthermore, it has been proposed to provide a composite elastic material comprising at least one gatherable web bonded to at least one elastic web, wherein the elastic web (which may comprise a fibrous web such as a nonwoven web of elastomeric fibers, e.g., meltblown elastomeric fibers) is tensioned to elongate it; the elongated elastic web is bonded to at least one gatherable web under conditions which soften at least portions of the elastic web to form a bonded composite web; and (c) the composite web is relaxed immediately after the bonding step whereby the gatherable web is gathered to form the composite elastic material. Such proposed method includes bonding the elongated elastic web to the gatherable web by overlaying the elastic and gatherable webs and applying heat and pressure to the overlaid webs, for example, by heating bonding sites on the elastic web to a temperature from at least about 65.degree. C. to about 120.degree. C., preferably from at least about 70.degree. C. to about 90.degree. C. In such proposed method, the elastomeric fibers may be formed from (1) A-B-A' block copolymers, wherein A and A' may be the same or different endblocks and each is a thermoplastic polymer endblock or segment which contains a styrenic moiety such as polystyrene or polystyrene homologs, and B is an elastomeric polymer midblock or segment, e.g., a midblock selected from the group including poly(ethylene-butylene), polyisoprene and polybutadiene, or (2) blends of one or more polyolefins with the A-B-A' block copolymers, the polyolefin being selected from one or more of polyethylene, polypropylene, polybutene, ethylene copolymers, propylene copolymers and butene copolymers. The gatherable web can be a nonwoven, non-elastic material, preferably one composed of fibers formed from materials selected from the group including polyester fibers, e.g., poly(ethylene-terephthalate) fibers, polyolefin fibers, polyimide fibers, e.g., nylon fibers, cellulosic fibers, e.g., cotton fibers and mixtures thereof. In connection with this proposed composite elastomeric material and method, note U.S. patent application Ser. No. 760,437, filed July 30, 1985, of Jack D. Taylor and Michael J. Vander Wielen, for "Composite Elastomeric Material and Process for Making the Same", the contents of which are incorporated herein by reference.
In this proposed method for making composite elastomeric materials, bonding between the layers of the laminate are provided by means of, for example, thermal bonding or ultrasonic welding, which will soften at least portions of at least one of the webs, so as to effectuate bonding by heat application and pressure. Due to the bonding of the films with heating, and since the elastomeric film is bonded in its stretched state, the difficulty arises that such bonding while applying heat renders the elastomeric web susceptible to losing its ability to contract if it is allowed to cool, even briefly, in the stretched condition. A proposed technique for overcoming this difficulty is to allow the composite web to immediately contract after bonding. However, such requirement to immediately relax the composite after bonding imposes an additional condition on the procedure. Moreover, additional problems arise due to use of heating during bonding. Thus, the number of breaks of the web are disadvantageously high, and burn-through (aperturing of the elastomeric web at the bonding points) and undesirable re-setting of the elastomeric meltblown occur due to the relatively high bonding temperatures.
Furthermore, utilizing, e.g., KRATON.RTM./polyethylene blends for forming the elastomeric web, it is very difficult to bond such elastomeric web to various desirable materials, such as spunbond polypropylene, as, e.g., the gatherable web of the composite material.
Various pressure-sensitive adhesive compositions are known. For example, U.S. Pat. No. 4,294,936 discloses pressure-sensitive adhesive compositions comprising (1) a synthetic rubbery thermoplastic block copolymer, e.g., an A-B-A or A-B block copolymer, where the A blocks are thermoplastic blocks and the B blocks are rubbery blocks and may be linear, branched or radial, or a mixture thereof; (2) a non-rubbery polymer which is preferably a copolyester, e.g., one of at least two different ester units; and a tackifier resin. As examples of the block copolymers are described KRATON.RTM.1102 (a styrene-butadiene-styrene block copolymer) and KRATON.RTM.1107 (a styrene-isoprene-styrene block copolymer). As the non-rubbery component is disclosed a copolyester, although polyethylene and polypropylene may be used. As the tackifier resin is disclosed rosin and dehydrogenated rosin, and oil soluble phenol-formaldehyde resins, among others. This patent further discloses that the adhesive composition can be applied by blending and melting the materials in an extruder and directly coating onto a suitable backing; and that the adhesives may be applied to, inter alia, non-woven fabrics.
U.S. Pat. No. 3,783,072 discloses processes for producing normally tacky and pressure-sensitive adhesive sheets and tapes, by extrusion, wherein a blend of A-B-A block copolymer (wherein A is a thermoplastic polymer block derived from styrene and B is an elastomeric polymer block derived from isoprene) and a solid tackifier is extruded onto a backing sheet. As the tackifier agent is disclosed conventional compatible solid tackifier agents including hydrocarbon resins or the like. KRATON.RTM.1107 thermoplastic elastomer block copolymer is disclosed as a material which can be utilized in the described adhesive formulation.
U.S. Pat. No. 4,543,099 discloses pressure-sensitive adhesives for imparting elastic characteristics to materials which are relatively inelastic, by extruding hot melt pressure-sensitive adhesive into contact with a substrate, the hot melt pressure-sensitive adhesive comprising (1) a rubbery block copolymer which includes a rubbery midblock portion terminated with crystalline vinyl arene blocks; (2) a tackifying resin generally compatible with and generally associated with the midblock portion of the block copolymer; and (3) an aromatic, essentially hydrocarbon resin having a glass transition temperature and a softening point above those of the tackifying resin and the endblocks of the block copolymer. This patent discloses that the block copolymers which can be used include KRATON.RTM., and the tackifying resins can include natural and synthetic essentially hydrocarbon resins.
U.S. Pat. No. 4,539,364 discloses hot melt sizes for glass fibers, applied as a hot melt to the glass fibers as they are formed so as to provide a coating on the glass fibers. The described hot melt size consists of a thermoplastic, block copolymer rubber, such as KRATON.RTM.; a low molecular weight polyethylene wax; and any low molecular weight resin compatible with the end styrenic block of the rubber block copolymer, the resin preferably being a hydrogenated styrene/methyl styrene copolymer having a weight average molecular weight of about 1000, a melt viscosity of 1 poise at 209.degree. C., and a glass transition temperature of about 65.degree. C., one particularly suitable hydrocarbon low molecular weight resin being REGALREZ.RTM. resin 1126 available from Hercules Incorporated.
Despite the foregoing, a void exists with respect to elastomeric composite materials (e.g., elastomeric composite laminates) that can be easily manufactured and that have desirable properties. Moreover, a void exists with respect to extrudable compositions for forming elastomeric sheet materials, e.g., for such composite materials, that can be used to easily form the elastomeric sheet materials (e.g., fibrous nonwoven webs such as meltblown webs). Furthermore, a void exists with respect to such elastomeric sheet materials which can be used to impart elastomeric properties to a composite laminate, with bonding between the elastomeric sheet material and another sheet (e.g., web) of such composite laminate being accomplished without the necessity of high temperatures.